Email does not support relative links since there is no implicit host. Therefore all links inside of emails must be fully qualified URLs. All path helpers are now deprecated. When removed, the error will give early indication to developers to use `*_url` methods instead.
Currently if a developer uses a `*_path` helper, their tests and `mail_view` will not catch the mistake. The only way to see the error is by sending emails in production. Preventing sending out emails with non-working path's is the desired end goal of this PR.
Currently path helpers are mixed-in to controllers (the ActionMailer::Base acts as a controller). All `*_url` and `*_path` helpers are made available through the same module. This PR separates this behavior into two modules so we can extend the `*_path` methods to add a Deprecation to them. Once deprecated we can use this same area to raise a NoMethodError and add an informative message directing the developer to use `*_url` instead.
The module with warnings is only mixed in when a controller returns false from the newly added `supports_relative_path?`.
Paired @sgrif & @schneems
When optimized path helpers were re-introduced in d7014bc the test added
in a328f2f broke but no-one noticed because it wasn't being run by the
test suite.
Fix the test by checking for nil values or empty strings after the args
have been parameterized.
